The overall objective is to use computer assisted reconstruction of neurons physiologically studied in alert animals and injected with horseradish peroxidase (HRP), to understand the neural basis for the generation and control of eye movements and vestibular reflexes. Alert squirrel monkeys will be employed in paradigms to physiologically identify neurons in relation to gaze and/or vestibular stimulation. Once identified, individual neurons will be injected with HRP intraaxonally to visualize somadendritic and axonal morphology. Intrasomatic recording and HRP injection in anesthetized, paralyzed animals will be used to supplement structure-function studies when appropriate. Neurons will be reconstructed using light microscopy aided by a three dimensional computerized system. Once morphological parameters of single cells have been entered into digital memory, we will quantitate the morphological interrelationships of the somata and dendritic and axonal trees of central neurons to ascertain if there are any orderly relationships. We will also determine the relationship of axonal terminal arbors of presynaptic neurons to dendritic arbors of post synaptic cells to infer connectivity and establish sequential neuronal order necessary for the information processing which enables the vestibular and oculomotor systems to perform their diverse functions. The brainstem is an ideal neural substrate in which to perform these studies because of the stereotyped and machine-like nature of many of its functions. These studies are a natural extension of ongoing projects in this laboratory that span nearly twenty years.